1. Field of the Invention
The present invention relates to a driving device for an automated endodontic procedure.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Various devices have been proposed to automate the endodontic procedure, first by proposing a head for driving cutting instruments via an alternating rotation, of equal amplitude, of these instruments. Failures were observed because, during the significant friction of the blades of the files on the intraductal dentin, the alternating rotating movements were causing fractures of the files engaged in the channel. Other failures were observed, such as false channels in the ductal curves or perforations.
Since instruments have been placed on the market that are manufactured from specific nickel titanium-based metals, the continuous, slow rotation of instruments suitable for cutting has been proposed using counter-angles producing this slow rotation. However, faced with constant failures, in particular instrument fractures on curved channels, automation by partial alternating rotation was once again proposed in documents EP 2,438,884 and US 2012/107766, in the hopes of minimizing the aforementioned drawbacks through the combined use of nickel titanium instruments.
Another alternative was proposed by the present inventor, and is based on a study of the instrumental dynamics during different phases of the endodontic procedure. This research led to patent EP 0,161,196, but above all to publications in specialized journals, for example Information Dentaire dated Jun. 05, 1986 no. 23 under the title: “Etude fondamentale sur le principe de fonctionnement d'un système automatisé” [Fundamental study on the operating principle of an automated system]. The principle consists of allowing an alternating translational movement of variable amplitude based on the resistance encountered by the blades of a file during its axial movement, and above all allowing a helical movement from the translational movement, since the resistance forces encountered by said inclined blades of the file on the walls of the channel drive the rotation of the file. This helical movement will have a more or less pronounced rotation based on the cutting resistance forces of the blades or during the movement of the file. The file should therefore be given rotational freedom during its movement.
To allow both the alternating translational movement of variable amplitude and this rotational freedom simultaneously, a driving head has been proposed including a body provided with a cavity receiving an instrument holder core coupled to driving means making it possible to communicate alternating axial movements thereto, where said instrument holder core is arranged on the one hand so as to allow an alternating movement of the instrument along its longitudinal axis, and on the other hand so as to impart a freedom of rotational movement around said axis to said instrument.
To that end, the driving axis is equipped with an eccentric housed in a slit or groove housed in the cylindrical instrument holder core. This groove has a length smaller than a 180° arc and a height with relatively significant play between the eccentric and one or the other of the upper or lower walls of the groove.
The minimum amplitude of the alternating longitudinal movements corresponding to the eccentricity of the eccentric is set at 0.5 mm and a maximum amplitude corresponding to the eccentricity increased by the value of the play existing between the walls of the groove and the eccentric is, for a play of 0.75 mm, a total of 1.25 mm.
Three types of problems are encountered when using such an assembly:
First, when a Hedstroem file, instrument whose blades are active in traction and inactive on descent, mounted on such a counter-angle, encounters strong resistance during traction for cutting of the intraductal dentin (therefore during raising of the instrument holder core), and the instrument cannot rise, the counter-angle will be driven depthwise, and could exceed the authorized working length if the operator cannot hold back this descent.
Secondly, there is cause to cite the unpleasant impression experienced by patients under certain circumstances, in particular when using a K-type file that encounters an obstacle: brutal shrinkage of the canal lumen, or calcification of this lumen, or when the diameter of the file is inappropriate for the empty ductal space: the tip of the instrument will strike the obstacle or the ductal walls, creating an unpleasant vibration for the patient. Some call this the jackhammer effect.